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I'm writing a fantasy novel and in it I'm designing a huge wooden ship moved by sail and man powered wheel paddle, and I wonder if it would be possible for the ship to carry a ballista inside that fires from the ship's prow? How effective were balistas against ships hull? How powerful was the largest ballista ever known? Sorry for the many questions and thanks in advance.

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  • $\begingroup$ Sounds plausible to me. As long as it's a strong ship and the ballista's not excessively heavy, it should be able to fit. A small-ish one would be effective against ships (So would a big one, but lighter is better for transportation.) $\endgroup$ – SealBoi Apr 22 '18 at 14:20
  • $\begingroup$ What era of technology? $\endgroup$ – RonJohn Apr 22 '18 at 14:25
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    $\begingroup$ Also, ballista have "wings" that spread out when fired, whereas ships' prows come to a point. Those two geometries aren't compatible. $\endgroup$ – RonJohn Apr 22 '18 at 14:26
  • $\begingroup$ Could you expand on the why? The prow is in the way of the projectile, and the arms of the ballista will collide with the sides of the hull, if it is indeed a huge ballista. If it is not huge, why carry it inside? If it is about surprise, you might consider raising it to the deck, already cocked. If it is about maximising the weapons' size, maybe something like a completely overpowered torsional catapult would do the trick? $\endgroup$ – bukwyrm Apr 22 '18 at 19:57
  • $\begingroup$ In order for this to be reasonably answerable I think you need to specify what type of ballista you envision. Will it fire bolts or rocks? Forward or more "up"? How far? $\endgroup$ – pipe Apr 22 '18 at 21:20
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Is it possible, inside?

Sure, many ships actually did carry ballista, though those were normally on the deck rather than inside, but inside is still a deck, just means it's a covered deck.

But on the top deck rather than a lower deck you potentially have a full three sixty degrees you can target by just swiveling your ballista without having to change course & swing the whole boat about, so it seems a bit silly to put it below decks if you only have the one ballista.

If you're using multiple small ballista it makes more sense to follow the pattern adopted by cannon bearing ships, rank them along the sides so you can bring more of them to bear on a single target simultaneously.

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    $\begingroup$ The other thing about the ship interior at the prow is there is probably a structural beam running down the midline of the ship. That would be in the middle of the 90 degree range you probably would have from that position. But cannons were put below deck - why? My prediction: only ships with many cannons had them below deck. Ships with one or two would have them up on top. $\endgroup$ – Willk Apr 22 '18 at 17:05
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    $\begingroup$ Cannon were below decks to reduce top hamper and prevent the ship from rolling over. $\endgroup$ – Thucydides Apr 22 '18 at 20:55
  • $\begingroup$ @Willk There is - but it runs along the bottom of the hull, and the keel attaches to it. There may be side-to-side beams, but not a front-to-back beam. Cargo vessels would often have no deck at all over the cargo-carrying section, making it easier to load and unload, and also making the vessel cheaper to build. $\endgroup$ – Graham Apr 22 '18 at 22:06
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In classical times, Roman ships carried torsion powered catapults as their primary weapon.

Roman warships evolved to become larger and have broader beams in order to become stable fire platforms for these weapons, but this may have been co evolution due to the Roman idea of using Marines to board enemy ships: lager ships could also hold more troops, and would also be more stable if a boarding platform like a Corvus was mounted.

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Diagram of a Corvus*

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Ancient Greek trireme. The ship is the weapon

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Roman "Decres". You can see the huge increase in size and provision for catapults on the deck. The smaller "Liburna" became the mainstay of the fleet after the Romans cleared the seas of pirates, and had no significant opposition

This leads to an important question in your worldbuilding: why does your navy feel the need for such large ships? What advantage do larger, more expensive, ships offer which smaller, cheaper ships do not? As an example, the Venetian "Arsenal" had several large "Galleasses" which were converted into mobile artillery platforms for the Battle of Lepanto. The Venetian merchant fleet had no use for them as the expense of running them ate any profits they might achieve, and the Venetian navy was dubious about their utility due to their size and slowness. Their use as artillery platforms was fortuitous, since there were only six, and indeed they were so slow they only were able to participate in the opening phase of the battle.

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Model of a Venetian Galleasses

So while your ship seems to be possible in theory, what practical use does it serve which cannot be carried out by smaller, cheaper ships? The polity which owns the ship or creates the navy will be very keen to find the cheapest, most practical means of carrying out the task, and if there are suitable alternatives, then they will take them over the larger, more costly ship.

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  • $\begingroup$ In the age of sail, "third-rate" ships were most effective per cost and easier to handle. $\endgroup$ – o11c Apr 22 '18 at 23:10
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How powerful was the largest ballista ever known?

According to Vitrubius (On Architecture, X, 11), the largest Roman ballistae fired stones of 250 pounds.

A catapult this size is an awful idea in a ship: with so much weight it probably took half an hour to fire each shot. It isn't a serious problem in a siege but, since the attack speed of a warship was 8-10 knots, you might want to settle for smaller siege equipment.

I think the standard ballista in a Roman ship shot stones of 40 pounds at distances inferior to 400 yards.

How effective were balistas against ships hull?

They weren't designed for breaching the hull (for that they rammed the ship or broke her oars). They were for killing the sailors on board, which is the reason javelins were also used as ammo for ballistae in ships according to Julius Caesar. There were around 100-120 soldiers on a warship, so killing a score of them with some shots was very effective for morale.

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    $\begingroup$ @Pelinore Wrong. A catapult is a machine that throws something (en.m.wiktionary.org/wiki/catapult). A ballista, an onager, a mangonel and a trebuchet are kinds of catapults. $\endgroup$ – Alberto Yagos Apr 23 '18 at 1:43
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    $\begingroup$ A mangonel is what most think of as a catapult while a trebuchet is a catapult that uses a counterweight rather than torsion energy, both are indirect fire weapons used to throw stones with an arm. A ballista is a completely different beast, essentially a giant crossbow used to hurl bolts (not stones) & more a direct fire weapon, your answer clearly showed you thought ballista are essentially the same as the first two (comments about time loading & firing stones etc), if you don't know don't answer the question. $\endgroup$ – Pelinore Apr 23 '18 at 7:15
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    $\begingroup$ @Pelinore A ballista has a similar launching action to a Springald, a large form of catapult or slingshot - and an aircraft catapult certainly doesn't have a throwing-arm $\endgroup$ – Chronocidal Apr 23 '18 at 7:17
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    $\begingroup$ @Chronocidal : A modern short take off aircraft launching system isn't relevant to the subject (regardless of having "catapult" in its name or not) and a springald isn't a ballista, which is what the question is about & so what the answers should be about, he gave an answer as if the question was about some siege weapon other than a ballista, simple as. $\endgroup$ – Pelinore Apr 23 '18 at 7:26
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    $\begingroup$ @Pelinore I was merely demonstrating that a non-swinging bow-or-slingshot type weapon is correctly described as a catapult (first example? "Ballistae"), rather than purely being the domain of an Onager or Trebuchet style seige weapon. This answer is about a ballista, your complaints seems to entirely that he (correctly) referred to it as a catapult (which is what the Romans would have called any "hurling" weapon) $\endgroup$ – Chronocidal Apr 23 '18 at 7:26

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